1. Field of the Invention
The present invention relates to a semiconductor device and method for fabricating the same, and in particular, to a bipolar-CMOS (complementary metal-oxide-semiconductor transistor)-DMOS (double diffused metal-oxide-semiconductor transistor) (BCD transistor) and method for fabricating the same.
2. Description of the Related Art
A bipolar-CMOS (complementary metal-oxide-semiconductor transistor)-DMOS (double diffused metal-oxide-semiconductor transistor) (hereinafter “BCD”) process, which was developed by ST Microelectronics corporation, is used for system on chip (SoC) product fabrication. ST Microelectronics's BCD process, combines fabrication of bipolar, CMOS and DMOS processes for a single device.
The BCD process is used for high voltage, high power and high integration density. For requirements of high voltage, a reduced surface field (RESURF) of a device is needed. FIG. 1 is a conventional P-type BCD transistor 150. During the conventional BCD process, an N-type buried region 103 is needed to be formed in a substrate 100 and an epitaxial layer 102 by ion implantation and diffusion processes. Also, an N-type isolation region (N-ISO region) 104 is formed in the epitaxial layer 102, which is connected to the N-type buried region 103. Next, a drain region 108, a lateral diffused drain region 109 and a source region 110 are formed in a portion of the epitaxial layer 102 surrounding by the N-type buried region 103 and the N-ISO region 104. In the conventional BCD process, the drain region 108 and the surrounding lateral diffused drain region 109 are used for RESURF requirements. The lateral diffused drain region 109 has less dopant concentration than the drain region 108, thereby resulting in a high breakdown field (BVdss), increased chip area and increased on resistance (Ron). Thus, typically, conventional BCD transistors have high Ron/BVdss ratios, thereby having less reliability.
Therefore, a semiconductor device and method for fabricating the same with high breakdown field (BVdss) and low on resistance (Ron) is needed.